1. Field of the Invention
The present invention relates to a magnetic head used for a magnetic storage device, and to a substrate for fabricating a magnetic head thereon.
2. Description of the Related Art
Various record/reproduce magnetic heads for a high capacity storage medium are used to record images in 8-mm video tape recorders or electronic still cameras and to record data in general hard disks or video or digital-audio flexible disks. Recently, a packing density in magnetic-recording devices has been rapidly improved and thin-film magnetic heads using a thin film magnetic device such as MR device are used instead of conventional ferrite core magnetic heads.
Slider material for the thin-film magnetic heads is required high wear resistance, surface smoothness on the air bearing surface, and also high machinability and milling characteristics including ion milling and reactive ion etching (RIE). To meet the above requirements, alumina-titanium-carbide-based ceramics is used to form the slider material.
Today, technologies of magnetoresistive (MR) or giant magnetoresistive (GMR) sensing devices using magnetoresistive effect have been introduced into magnetic head devices to improve packing density of the storage systems. On one hand, to improve read-sensitivity of MR devices, the sensing current must be increased from MR devices. On the other hand, to improve the recording density on the storage media, it is necessary to reduce a magnetized volume in the medium on a magnetic disk. In the case of the MR head slider for hard disk drive, a levitation of the head slider reaches approximately 1 xcexcm from the storage surface of the disk, which is close to a near-contact, and then a temperature of the MR device tends to vary due to the degree of near contact with the medium during sliding.
With decrease in magnetized volumes of a medium, the magnetizing direction of a pin layer becomes more unstable resulting in deteriorated head performance. This thermal asperity phenomenon also has been a important problem and heat radiation characteristic around an magnetic device mounted on the magnetic head must be improved.
To improve heat radiation characteristic around a magnetic device, a gap layer has been formed of AlN or DLC having a high thermal conductivity. An amorphous alumina on an Al2O3-TiC-based substrate has been decreased in thickness. These solutions allow an MR device to approach an Al2O3-TiC substrate, having an effect for improving heat radiation from the devices. Moreover, many recesses occurring due to a hardness difference between an Al2O3-TiC substrate and an alumina layer can prevent an MR device from colliding to a medium face. Also, heat radiation characteristic has been improved by interposing a DLC layer having a high thermal conductivity between an amorphous alumina layer and an Al2O3-TiC-based substrate.
However, because it is not enough only to improve the heat radiation characteristic around an device, a high heat radiation characteristic is requested for a substrate. A conventional Al2O3-TiC-based substrate material has a low thermal conductivity of approximately 25 W/m.K, obtaining an insufficient heat radiation characteristic as the whole of a magnetic head even though a high-thermal conductivity layer is formed on such a substrate.
Therefore, as an attempt of applying a silicon carbide sintered body having a high thermal conductivity to a magnetic recording part because a substrate material has a preferable heat radiation characteristic, a sintered body added with a sintering agent is disclosed in Japanese Patent Publication No. 63-128885/1988. Moreover, Japanese Patent Publication No. 5-258241/1993 discloses a slider of a magnet head formed on a sintered body containing a combined phase of an SiC-Al-O-N phase and a TiN/TiC phase. Also, Japanese Patent Publication No. 10-251086/1998 discloses a silicon carbide reaction-sintered body impregnated with silicon (Si) being used as a slider.
Magnetic heads are generally fabricated as described below. First, a substrate having a diameter of 3 in. to 6 in. is provided with an insulating underlayer by alumina sputtering on its body surface. Thousands of magnetic devices such as MR devices are formed on the insulating film using a lithography technique, and then, another insulating alumina layer is covered over the devices over the surface of the substrate. The Substrate is cut to separate bars each including a plurality of the magnetic devices, considering a polishing margin for sliders. The bar is precisely mirror-machined on one of cut-out faces to form an air bearing surface and grooved through ion milling or reactive ion etching (RIE) at a high accuracy to form a negative pressure portion on the air bearing surface, and thereafter is divided to each magnetic head.
However, because the silicon carbide sintered body in which silicon is impregnated disclosed in Japanese Patent Publication No. 10-251086/1998 is a mixture of silicon and silicon carbide grains, these two phases are different in hardness, and different in lapping rate or ion-milling rate during mirror machining in the negative-pressure portion, causing steps on surfaces of the substrate to occur easily after machining, therefore, the sintered body not being practically used.
Moreover, known silicon carbide sinters use a sintering agent such as alumina or yttria, as disclosed in Japanese Patent Publication No. 63-128885/1988. A grain-boundary phase of the sintered body contains a composite oxide as a reaction product of an agent and silica in silicon carbide grains, and therefore the differences of hardness and milling characteristics between the grain-boundary phase and the silicon carbide grain roughen the polished surfaces of the sintered body.
Moreover, silicon carbide sintered bodies often contain boron or carbon as a sintering agent, but more carbon may be added as an indispensable component so that free carbon remains in the form of individual grains in the sintered body. As a result, machinabilities differ of remaining carbon grains and silicon carbide grains due to difference in hardness and chemical properties and a great number of voids are produced in the polished surface after machining.
It is an object of the present invention to provide a magnetic head slider capable of preventing voids or steps from being produced after mirror machining or ion milling, improving the precision machinability, and achieving dense and superior smoothness.
It is another object of the present invention to provide a substrate insulated from a magnetic shield, preventing an device from contacting a medium face, and having an amorphous insulating layer superior in contact strength, electrical withstand voltage, and face quality.
The present invention is realized as a result of studying various materials having a thermal conductivity and a volume resistivity necessary for a magnetic-head substrate and a magnetic head and moreover having preferably strength and sliding characteristic, and thereby knowing that the above object can be achieved by controlling the purity, denseness, and other characteristics of silicon (Si) carbide in a specific range.
A magnetic-head substrate of the present invention is made of ceramics containing 99 wt % of silicon carbide or more and 0.3 wt % of free carbon or less, and having a relative density of 99% or more.
Moreover, a magnetic head of the present invention is constituted by forming alumina, AIN, or BN serving as an insulating underlayer on a magnetic-head substrate of the present invention.